The disclosure of Japanese Patent Application No. 2000-315095 filed on Oct. 16, 2000, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a hybrid vehicle that is driven by any suitable combination of an internal combustion engine and an electric motor, in view of saving of energy resources and environmental protection, and in particular to such a hybrid vehicle with improved engine revolution performance and improved emission control at cold starting of the internal combustion engine.
2. Description of Related Art
It has been proposed to temporarily stop an internal combustion engine of a vehicle, such as an automobile, during an operation of the vehicle, for the sake of savings of energy resources and environmental protection, when certain conditions under which the engine is allowed or desired to be temporarily stopped are established. In fact, this technology has been implemented in some types of automobiles. The conditions for temporarily stopping the engine may be established when, for example, the vehicle stops at a red traffic light, or the vehicle stops or travels at a considerably low speed because of a traffic jam, or the like.
The above-described technology of temporarily stopping the engine may be employed in a hybrid vehicle including an engine, an electric motor, a generator and a battery. In the hybrid vehicle, power can be transmitted among the engine, the motor and the generator, and the motor uses the battery as an electric power supply. The hybrid vehicle may be driven by one or both of the engine and the motor. Namely, the hybrid vehicle runs by means of a selected one or both of the output of the engine and the output of the motor. Furthermore, the generator is driven when appropriate by utilizing one or both of the output of the engine and the inertia of the running vehicle, so as to charge the battery. A known example of a hybrid vehicle is disclosed in Japanese Laid-open Patent Publication No. 7-255104.
The aforementioned hybrid vehicle is driven by starting the engine that can be stopped temporarily during operation. The structure of the hybrid vehicle as described above is based on a general concept of the hybrid vehicle that is essentially driven by the engine but can be partially driven by a motor that assists the engine in driving the hybrid vehicle. In the above-structured hybrid vehicle, when start of the engine is required again to drive the vehicle, the engine in a stopped or a cold state has to be warmed up as quick as possible for resuming its normal condition.
On the other hand, the hybrid vehicle also can be started by the motor alone, even if the engine is in the stopped state. Accordingly the hybrid vehicle may be structured so as to be driven by starting the motor instead of the engine. If the engine is sufficiently preheated before driving the vehicle, the engine can be smoothly so operated and accordingly, emissions of harmful components in the exhaust gas during cold start of the engine can be reduced.
In view of the foregoing characteristics of the hybrid vehicle, it is an object of the invention to provide a hybrid vehicle with improved revolution performance and emission of the exhaust gas during cold start of the engine.
The foregoing and/or other objects are achieved by a hybrid vehicle including a power train including an engine, a battery and a motor, and which is selectively driven by at least one of the engine and the motor using the battery as a power supply. A heat accumulator holds at least a portion of a cooling water of the engine to be kept warmed. A pump feeds the cooling water held in the heat accumulator into the engine. An engine starting unit includes at least one of the motor and an electrically operated starter, a key switch that is turned on by a vehicle operator during operation of the vehicle, and a power supply controller that brings the motor into an operating state for driving the vehicle in response to turn-on of the key switch, and starts the engine. The power supply controller operates the pump to feed the warmed cooling water in the heat accumulator into the engine upon the turn-on of the key switch, and operates the engine starting unit to start the engine upon an elapse of a predetermined time period after the warmed cooling water in the heat accumulator starts being fed to the engine.
In the above-constructed hybrid vehicle, the power supply controller is operative to actuate the engine starting unit when the cooling water in the engine reaches a predetermined temperature through an operation of the pump.
According to another aspect of the invention, the power supply controller is operative to actuate the engine starting unit upon detection that an operating amount of an accelerator pedal is equal to or greater than a threshold value even before the cooling water in the engine reaches the predetermined temperature or before the elapse of the predetermined time period that is estimated to be required for the cooling water in the engine to reach the predetermined temperature through operation of the pump.
According to another aspect of the invention, the power supply controller is operative to actuate the engine starting unit upon detection that a state of charge of the battery is equal to or less than a predetermined threshold value even before the cooling water in the engine reaches the predetermined temperature or before the elapse of the predetermined time period that is estimated to be required for the cooling water in the engine to reach the predetermined temperature through an operation of the pump.
According to another aspect of the invention, the power supply controller may be operative to cancel an actuation of the pump to be performed prior to driving of the engine starting unit when a state in which a temperature of the cooling water in the engine does not reach a predetermined temperature repeats a predetermined number of cycles after an elapse of the predetermined time period that is estimated to be required for the cooling water to reach the predetermined temperature.
As described above, the hybrid vehicle is driven by operating at least one of an engine and a motor using a battery selectively as a power supply. In most types of the aforementioned hybrid vehicles, an output required for the vehicle just after starting may be derived from the motor by itself. In the case where a cooling water temperature in a heat accumulator is higher than a cooling water temperature in the engine by a predetermined degree when a key switch is turned on, the pump is actuated to feed the cooling water in the heat accumulator into the engine such that the engine is pre-heated and then started by actuating a drive unit for starting the engine. More specifically, the engine can be preheated by the heat accumulated in the heat accumulator before starting the vehicle so as to realize smooth engine operation by reducing the viscosity of an engine oil, and reduction in emissions of harmful unburned component such as HC and CO by making the fuel in the cylinder more combustible without deteriorating an output performance of the vehicle.
In accordance with an aspect of the invention, the power supply controller serves to operate the drive unit for starting the engine even before the cooling water in the engine reaches the predetermined temperature or before an elapse of the predetermined time period that is estimated to be required for the cooling water in the engine to reach a predetermined temperature. As a result, an effect for preheating the engine by means of the heat accumulator is maximized while minimizing the delay in starting the engine.
However, according to one aspect of the invention, even before the cooling water in the engine reaches the predetermined temperature, or the elapse of the predetermined time period, the power supply controller may actuate the engine starting unit immediately after detection that a state of charge of the battery is equal to or less than a predetermined threshold value. Accordingly, when the state of charge of the battery is insufficient, that is, the motor by itself cannot supply sufficient power to satisfy the required vehicle output, the power supply controller is allowed to start the engine immediately by temporarily canceling preheating of the engine by the heat accumulator.
According to another aspect of the invention, the power supply controller may be constructed to cancel actuation of the pump to be performed prior to driving of the engine starting unit when a state in which a temperature of the cooling water in the engine does not reach a predetermined temperature repeats a predetermined number of cycles after an elapse of the predetermined time period that is estimated to be required for the cooling water to reach the predetermined temperature. Such construction is capable of preventing the device for preheating the engine from deteriorating the vehicle performance in case a failure occurs in the heat accumulating system, including the pump. The predetermined number of cycles may be set to at least one, as well as to any number, so long as the function of the preheating device is not deteriorated and the failure occurred in the system is overcome.